Plenty. The key word in the text of the Fourth Amendment is “unreasonable,” as in “unreasonable searches and seizures” that we have a right to be free from. A search without a warrant is presumptively unreasonable; so if particular police conduct is a “search,” they need a warrant to do it. If it’s not, they don’t.

So what’s a “search”?  In 1967, the Court, in Katz v. United States, a famous case involving hidden microphones placed in a phone booth, held that the Fourth Amendment protects each person’s “reasonable expectation of privacy.”  Now, for an originalist, the problem with “reasonable expectation of privacy” as a legal category is that it’s unavoidably pegged to evolving social standards.

The Katz Court didn’t hold—and couldn’t possibly have held— that a person has a right to be free from warrantless bugging in his phone booth conversations because that was the common understanding in 1791.  Instead, it held that a person has a right to be free from warrantless bugging—and dozens of other contexts in which the Katz test has subsequently been applied—because that is an expectation that “society is prepared to recognize.”

The Court has applied this framework to cell phones, computers, email, thermal imaging cameras, airplane overflights, you name it.

In other words, modern Fourth Amendment jurisprudence has built into its core analytic framework precisely the kind of “evolving constitution” that Scalia rails against in his standard college-audience stump speech.   So Scalia bided his time, and last year, after 25 years on the bench, he seized his chance to apply some originalism to the Fourth Amendment.

In January 2012, in a case called United States v. Jones, Scalia assembled a five-justice majority, Justices John G. Roberts, Thomas, Anthony Kennedy, and Sonia Sotomayor, for the brand-new rule that whenever police engage in conduct that would have been considered trespassing in 1791, and do so for the purposes of gaining information about crime, that’s a search.

The issue in Jones was whether it was a “search” to place a GPS tracker on someone’s car. Some readers may be surprised to learn that prior to Jones, this technique was not legally considered a “search,” and thus did not require a warrant or any degree of suspicion. You could (and like everyone else doing trafficking investigations, I did when I was a federal prosecutor) just slap one on and see where someone went.

Not any more.

In Jones, Scalia and his majority held that placing the tracker on the car was a physical appropriation of the property of the car’s owner, and that in 1791 this would have been considered a trespass.  Therefore it’s a “search” today. (The opinions actually discuss the likely 18th century view of the legal propriety of stashing a very tiny constable in someone’s carriage.)

Scalia didn’t have the votes to overrule the Katz “reasonable expectation of privacy” definition, so his new definition just supplements it: both definitions are now applicable, and the other four justices in Jones (Samuel Alito, Ruth Bader Ginsburg, Stephen Breyer, and Elena Kagan) also thought that placing a tracking device on a car was a “search” under the Katz test. That is, they would have held that people have a reasonable expectation that the movements of their car are not being tracked.

The really fascinating thing about the case for purposes of predicting the future course of the law is that Justice Sotomayor joined both groups: she voted with Scalia’s majority, but wrote a separate concurrence endorsing the Katz analysis.

So, since January 2012, if the police install a tracking device on your car, they have to get a warrant.

The day Jones was decided, I began wondering, along with probably most other people in the business, what Jones’ new “18th century trespass” test was going to mean for that other staple of police investigation, the “knock-and-talk.”

Before last Tuesday, the prevailing view in law enforcement and the courts was that the Constitution permits police officers to walk up to residences and knock on the door. In so doing, they are not constrained by formal concepts like property lines; rather, they cannot violate the owner’s reasonable expectation of privacy. So you tell your agents that if there’s a big fence and a gate with a “No Trespassing” sign, you can’t just open it and go in.

But if we’re talking about a typical suburban house with no fence and a nice walkway from the sidewalk to the front door, then sure, go ahead.  And if you happen to come upon any evidence (like something you see through the window while you’re standing at the front door), it’s fair game.

Unless the homeowner clearly signals his or her intent to keep the public away, then the public, including cops, can come and say hi.

The officers in Jardines pushed the “knock-and-talk” concept to its breaking point, and were, one has to admit, tempting constitutional fate: they were not going up to the front door to talk to the residents of the house.  They were going up to the front door to have a drug dog sniff around to see if marijuana odors were wafting from inside.

So the state was put in the position of defending their conduct under “knock-and-talk” principles when everyone knew it was something else. But whether that difference (intent to sniff rather than to say “hi”) made a constitutional difference was unclear.

Not any more.

Sure enough, Jardines is Jones’ second shoe. It starts off with a quote from Jones, and the holding is straight-up Jones: as a matter of traditional property law, a homeowner offers an implied license to the public to enter his or her property for particular purposes (bringing over a pie, say, or delivering the mail, or peddling Girl Scout cookies). Searching for evidence of crime is not one of those “traditional invitations.” Case closed.

What’s interesting about Jones and Jardines is that by applying 18th century common law to modern law-enforcement investigative techniques, the Court has now dramatically expanded the scope of individual civil liberties.

This doesn’t mean that all knock-and-talks now require a warrant, of course. But it does mean that the officers’ purpose in conducting the knock-and-talk is now the key to the admissibility of evidence obtained during the encounter. So prosecutors and defense attorneys had better be prepared to litigate claims of “pretextual” knock-and-talks whose real purpose was to “gather evidence.”  And it’s even possible that some courts may hold that even traditional knock-and-talks are “searches” under Jardines if, for example, the residence in question is that of a suspect. Lawyers: I think that argument could have legs in some cases, but the much tougher issue will be the “good faith” argument against suppression. If you have an arguably pretextual knock-and-talk that occurred after January 23, 2012, call me.

Jones and Jardines are huge, huge cases for the law of criminal investigations, and they signal that there is more to come, that the Court is prepared to further restrict the ability of the state to intrude into individual privacy without prior judicial oversight (a warrant).

That’s why it’s so fascinating—and maybe ironic, I suppose, depending on one’s politics—that the “What Would Thomas Jefferson Do?” methodology which seems so bizarre (to me, anyway) when talking about sexuality, gender, and race, has produced such strikingly civil-libertarian results in the criminal procedure arena.

Caleb Mason is an attorney at Miller Barondess LLP in Los Angeles, and a former federal prosecutor. He welcomes comments from readers.